Precipitation method of separation of neptunium



PRECIPITATION METHOD OF SEPARATION OF NEPTUNIUM Lawrence B. Magnusson, Richmond, Califi, assignor to the United States of America as represented by the United States Atomic Energy Commission No Drawing. Application February 2, 1948 Serial No. 5,890

3 Claims. (Cl. zap- 14.5

This invention relates to a method of separating neptunium from plutonium.

Plutonium exists in at least 'four valent states, plus three, plus four, plus five and plus six. Neptunium exists in at least three of these-valent states, plus four, plus five and plus six. The behavior of these two elements in the presence of various anions with or without a carrier cation depends upon the valent state of the elements and upon the solubility of the carrier formed. Thus fluorine ions form insoluble fluorides of the two elements in a valent state not greater than plus four. Also when these elements are in the plus six state of oxidation theyform insoluble complex acetates with alkali metals, and they. are carried from solution as sodium neptunyl acetate and sodium plutonyl acetate especially when sodium uranyl acetate is present as a carrier.

A process for the differential oxidation of neptunium B counts/min. of Np per ml. A lanthanum fluoride 7 carrier was precipitated by making the aliquots l M in HF. The lanthanum fluoride precipitate was separated by centrifuging and washed once with- 0.2 milliliter." of water.. The separated and washed precipitates were then mounted on platinumfoils and the neptunium and plu- '15 1i determining the number of ac counts of plutonium carried ions in the presence of plutonium ions and sulphate ions metal bromate. From such a treated solution, plutonium may be removed by adding lanthanum ions and fluoride ions and separating the lanthanum fluoride precipitate thus formed. This process requires one to two hours for the oxidation step which is carried out at room temperature.

The instant invention is an improvement over the invention just outlined, particularly in the speed of the process.

In accordance with this invention neptunium is separated from an aqueous solution containing neptunium, plutonium, and sulphate ions by contacting said solution with hypochlorite ions at room temperature, adding lanthanum ions and fluoride ions thus precipitating lanthanum fluoride and plutonium fluoride, and then separating the resulting precipitate and the supernatant solution.

The operation of this invention is illustrated by the following examples.

EXAMPLE I A stock solution was prepared .containing the following ingredients: NaClO, H 80 and La+ ions. Tracer neptunium and plutonium solution was prepared in acid solution .and the valent states of these two elements were reduced to a state not greater than plus four by contacting the solution with sulphur dioxide. The tracer solution containing neptunium and plutonium was then mixed with the stock solution and at the end of various time intervals (as shown by Table I) 1 milliliter aliquots of the mixed solution were withdrawn. The l-milliliter aliquots contained the following concentrations of ingredients: 0.15 M NaClO, 0.5 M H 80 0.2 mg. La+ /ml., 2370 on counts/min. of Pu per ml. and 1330 not greater than plus four.

tonium were determined by usual radiochemical techniques. Since neptunium is a beta emitter and plutonium is an alpha emitter, the quantities of these two elementsv present are readily estimated. This determination de-; pends upon the fact that reduced neptunium-and plutonium are carried by a lanthanum fluoride carrier precipitate, but oxidized neptunium and plutonium arenot carried by a lanthanum fluoride carrier. Thereforethe amount of each species oxidized was readily found by with the precipitate and the number of [3 counts of neptunium carried with the precipitate, since the percentage of each species which was oxidized was inversely propor-.

tional to the percentage of the total counts per minute 1 of the species present in the precipitate. :This is shown" in the column entitled Not oxidized by fClO-.'in

Table I. The combined supernatant solution and wash was then treated with sulphur dioxide to reduce any OXi? dized neptunium and plutonium present to a valent state After about a one hour reduction time about 0.2 milliliter of solution containing 0.4 milligram of lanthanum ions was added in three por-g tions to precipitatejlanthanum fluoride, which was separated and mounted on platinum foils and assayed by regular radiochemical techniques, thus giving a determination of the amounts of plutonium-and neptunium which had been oxidized by the'ClOio'n, and subsequently" reducedand precipitated. These results are summarized in the column entitled Oxidized by ClO- in Table I.

This table shows that 74 percent of the neptunium had been oxidized by the hypochlorite in 15 minutes, that 91 percent had been oxidized in 30 minutes, and that 97 per- .cent had been oxidized in one hour, contrasting to one percent or less of the plutonium oxidized in the same length of time. t

' Table I Oxidized by OlO- Not Oicgzed by Oxidation Time (Minutes) 7 Percent Percent Percent Percent Pu Np u D EXAMPLE II Hypochlorous ions will also diflerentially oxidize neptunium in the presence of macro quantities of plutonium. Thus a lanthantun fluoride precipitate containing 9850 milliligrams of plutonium and tracer quantities of neptunium was metathesized by slurrying with 10 liters of an aqueous solution containing 15 percent KOH and 10 percent K 00 at C. for four hours. The metathesized lanthanum-composition was 'dissolved in 10 N HNO This solution was contacted with 3 liters of hydrogen peroxide solution that was about 1.5 N in HNO and 0.1 Niin H SO thus precipitating the plutonium as PuO which carried the neptunium. The precipitate was dissolved in sulphuric acid and adjusted to a concentration of 1 N in H To this solution there was added 1 liter of 0.15 M NaOCl solution and the mixture was allowed to stand 8 hours. The oxidized 2,841,464 I -Pa.tented July 1, 8.

solution was then made 0.2 M in KP and 0.5 M in HF. Potassium plutonous fluoride was precipitated, leaving the neptunium in solution. The supernatant solution containing the neptunium was treated, With sulphur dioxide toreduce the neptunium and then lanthanum ions were added to a concentration of 100 milligrams per liter. The lanthanum fluoride precipitate carrying the neptunium was separated and assayed for neptunium by the usual radiochemical techniques. The results are summarized in Table II.

The data in Table II show that 90 percent of the neptunium present in the original lanthanum fluoride material remained in the supernatant solution from the potas'sium plutonous fluoride precipitation. About percent ofthe neptunium remained in the peroxide supernatant solution and the remainder had been lost in the metathesis steps or in other parts of the process.

Table II Plutonium, N eptunium, Process Step milligrams percent of original Original LaF Slurry 9, 850 100 Peroxide Preeipitate 9, 750 Peroxide Supernatant 120 5 KaPuFs Supernatant 3. 7 90 4 ment and the neptunium removed by addition of sodium ions and acetate ions thus carrying the neptunium down as the insoluble sodium neptunyl acetate.

What is claimed is:

l. A process for the separation of neptunium from plutonium in an aqueous solution containing neptunium ions in a valence state not greater than +4, plutonium ions in a valence state not greater than +4 and sulphate ions, comprising adding hypochlorite ions to said solution and then digesting the solution at. a temperature of 15 to 25 C., adding lanthanum ions. and fluorine ions, and thereafter separating the supernatant solution frorn the precipitate.

2. The process of claim 1 in which lanthanum nitrate is the source of the lanthanum ions and hydrofluoric acid is the source of fluorine ions.

3. A process for the separation of neptunium from plutonium in an aqueous solution contaning neptunium ions in a valence state not greater than +4, plutonium ions in a valence state not greater than +4 and sulphate ions, comprising adding hypochlorite ions to said solution, and then digesting the solution at 15 to 25 C., adding potassium fluoride and" hydrofluoric acid, and thereafter removing the potassium plutonous fluoride precipitate thus formed.

References Cited in the file of this patent Deming: General Chemistry, 5th ad, page 275 (19.44); publ. by John Wiley & Sons, New York.

Seaborg: Plutonium and Other Transuraniurn Ele- 

1. A PROCESS FOR THE SEPARATION OF NEPTUNIUM FROM PLUTONIUM IN AN AQUEOUS SOLUTION CONTAINING NEPTUNIUM TIONS IN A VALENCE STATE NOT GREATER THAN +4, PLUTONIUM IONS IN A VALENCE SATE NOT GEATER THAN +4 AND SULPHATE IONS, COMPRISING ADDING HYPOCHLORITE IONS TOT SAID SOLUTION AND THEN DIGESTING THE SOLUTION AT A TEMPERATURE OF 15* TO 25*C., ADDING LANTHANUM IONS AND FLUORINE IONS, AND THEREAFTER SEPARATING THE SUPERNATENT SOLUTION FROM THE PRECIPITATE. 